Original Paper Med Princ Pract 2005;14:16–21 DOI: 10.1159/000081918 Genotypic Diversity among Isoniazid-Resistant Isolates of Mycobacterium tuberculosis from Rashid Hospital in Dubai, United Arab Emirates Suhail Ahmad a Esther Fares b a Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait; b Department of Health and Medical Services, Rashid Hospital, Dubai, UAE Received: May 31, 2003 Revised: November 17, 2003 Dr. Suhail Ahmad Department of Microbiology, Faculty of Medicine Kuwait University, PO Box 24923 13110 Safat (Kuwait) Tel. +965 531 2300, ext. 6503, Fax +965 531 8454, E-Mail suhail_ah@hsc.edu.kw ABC Fax + 41 61 306 12 34 E-Mail karger@karger.ch www.karger.com © 2005 S. Karger AG, Basel 1011–7571/05/0141–0016$22.00/0 Accessible online at: www.karger.com/mpp Key Words Mycobacterium tuberculosis W Isoniazid resistance W Genotyping W katG gene W Dubai Abstract Objective: To perform molecular fingerprinting for strain relatedness among isoniazid-resistant Mycobacterium tuberculosis isolates recovered from tuberculosis (TB) patients in the United Arab Emirates (UAE). Materials and Methods: Thirty-two consecutive isoniazid-resistant M. tuberculosis strains isolated from TB patients (4 na- tives and 28 expatriates) at Rashid Hospital, Dubai, UAE were analyzed. The typing was carried out by touchdown double-repetitive-element PCR (DRE-PCR). The status of R463 or L463 polymorphism and the presence of S315T mutation in the katG gene were also determined for iso- lates exhibiting cluster pattern in DRE-PCR. Results: All the 32 isolates (28 from expatriate patients and 4 from UAE nationals) exhibited 21 distinct patterns in DRE-PCR with 20 of 32 isolates exhibiting unique patterns and the remaining 12 exhibiting cluster ‘A’ pattern. All the iso- lates (19 of 19) yielding two or more DNA fragments in DRE-PCR were unique strains. The genotypic heteroge- neity among 10 of the 12 cluster isolates was suggested by the varying susceptibility of these isolates to anti-TB drugs, presence of R463 or L463 polymorphism in the katG gene and the presence or absence of S315T muta- tion in the katG gene. Conclusion: The genotypic diversi- ty among isoniazid-resistant M. tuberculosis isolates mostly recovered from expatriate patients indicates that most expatriates were infected with a unique strain imported, most likely, from their country of origin and that their latent infection was reactivated in UAE. Copyright © 2005 S. Karger AG, Basel Introduction Tuberculosis (TB) caused primarily by Mycobacterium tuberculosis is an infectious disease of global significance. It is estimated that nearly 2 billion people are already infected with M. tuberculosis, 8 million individuals devel- op active disease and nearly 2 million people die of TB each year, mostly in developing but also in developed countries [1]. The emergence and spreading of drug-resis- tant strains of M. tuberculosis has become a major obsta- cle in the control and management of TB [2]. A better understanding of transmission patterns will help to con- trol the spread of infections, particularly involving drug- resistant strains of M. tuberculosis. Clinical isolates of M. tuberculosis are usually differentiated by Southern blot-